The present invention relates to a method and a device for selective laser sintering in which powder is introduced in layers into a jacketed design space, forming a powder cake which is consolidated layerwise using laser radiation.
Selective laser sintering (SLS) is a rapid prototyping method in which a platform (design space bottom) which can be lowered into a design space carries a powder layer which is heated by a laser beam in selected regions so that the powder particles fuse to form a first layer. Subsequently, the platform is lowered downward into the design space by approximately 50 to 200 μm (depending on the particle size and type), and a new powder layer is applied. The laser beam draws its path again, fusing together the powder particles of the second layer as well as the second with the first layer. In this manner, a multilayer powder cake and, inside of it, a component such as an injection mold are formed little by little.
Inside of the design space, specific regions undergo a heating by the laser beam for a longer or shorter period of time, depending on the geometry of the component to be manufactured, whereas others are not heated at all. Moreover, in each case only the uppermost powder layer is heated by the laser; the lower layers give off the absorbed heat to their surroundings and cool off. The consequences include inhomogeneous temperature distributions and thermal stress within the powder cake which may result in component distortion.
To minimize this problem, it was already proposed in European Patent Document EP 556 291 to adjust a uniform base temperature of the respective surface layer, using a ring-shaped radiant heater mounted parallel to and above it. The intended result is a more uniform cooling of the individual layers and, consequently, less component distortion. This European Patent Document is related to U.S. Pat. No. 5,155,321, which is hereby incorporated by reference herein.
However, several tests have shown that temperature gradients still occur within and between the individual layers of which, in particular, those mentioned first result in component distortion which is not tolerable at least in the case of high-quality components.